Confirm that the VPN is connected to the external VPN server (whatismyipaddress.com should show the IP address of the VPN server), that VPN Policies are turned off on the GL-MT1300, and that the GL-MT1300 is in Repeater/Router mode (the 2 computes are on different subsets).

Can you post the output of traceroute from Computer B to Computer A (run tracert in Windows)?

I do not work for and I am not directly associated with GL.iNet